205653-84-5Relevant academic research and scientific papers
Kinetics and Mechanisms of Hydrogen Peroxide Disproportionation Catalyzed by Mononuclear Schiff Base Manganese(III) Complexes: Effects of Chelate and Hydroxide Ion on Hydrogen Peroxide Disproportionation in N,N-Dimethylformamide
Uehara, Minori,Urade, Mika,Abe, Yuriko
, p. 609 - 617 (1998)
The preparation of [Mn(saltnOCOPh)Cl]·DMF (H2saltnOCOPh: N,N'-(2-benzoyloxypropane-1,3-diyl)bis(salicylideneamine)) and kinetics and mechanisms of H2O2 disproportionation catalyzed by mononucleur Schiff base manganese(III) complexes, such as [Mn(salen)Cl) (H2salen: N,N'-ethylenebis(salicylideneamine)), [Mn(saltn)Cl] (H2saltn: N,N'-propane- 1,3-diylbis(salicylideneamine)), [Mn(saltnOH)Cl] (H2saltnOH: N,N'-(2-hydroxypropane-1,3-diyl)bis(salicylideneamine)), and [Mn(saltnOCOPh)Cl] in N,N'-dimethylformamide (DMF), have been investigated. The disproportionation of H2O2 to O2 and H2O proceeds coupled with the redox cycle between the Mn(III) complex and the Mn(IV) intermediate: The first step is the fast equilibrium (Km) of the Mn(III) complex and the Mn(IV) intermediate formed by the reaction of the Mn(III) complex with H2O2, followed by a slow reaction (k1) of the Mn(IV) intermediate with H2O2 to produce O2 and H2O recovering the original Mn(III) complex. The Km values decrease in the following order: [Mn(salen)Cl] (728 mol-1 dm3) ? [Mn(saltnOH)CI] (28.0 mol-1 dm3) > [Mn(saltn)Cl] (6.28 mol-1 dm3) > [Mn(saltnOCOPh)Cl] (1.83 mol-1 dm3), reflecting an increased distortion along the axis containing the coordination of H2O2 to the Mn(III) complex. On the other hand, the rate constants (k1) fall into the following sequences: [Mn(saltnOH)Cl] (4.29 × 105 mol-2dm6s-1) > [Mn(salen)Cl] (1.67 × 105 mol-2 dm6 s-1) > [Mn(saltnOCOPh)Cl] (3.34 × 104 mol-2 dm6 s-1) > [Mn(salen)Cl] (6.15 × 103 mol-2 dm6 s-1). In spite of the small Km values for saltnOH, saltnOCOPh, and saltn complexes with the 1,3-diamine ligand, compared to that for the salen complex, the large kl value for the saltnOH complex strongly suggests stabilization of the transition state for the formation of hydrogen-bondings among the Mn(IV) intermediates and H2O2. Futhermore, the effect of the OH- ion on the H2O2 disproportionation catalyzed by [Mn(salen)Cl] has been reported. On account of the formation of [Mn(salen)OH] coordinated by the OH- ion, the appearance of the reaction path involving not only the Mn(III)-Mn(IV) cycle, but also the Mn(II)-Mn(III) cycle, is shown based on the ESR and visible spectral studies. The activity for the Mn(II)-Mn(III) cycle is 20 times larger than that for the Mn(III)-Mn(IV) cycle.
